An essential feature of an irrigation system of the trickle type is the use of a metering orifice capable of limiting flow rates to very small flow rates, for example of the order of two or three liters per hour from a supply pressure of about 100 k Pa.
One of the most successful metering devices presently used comprises a length of fine bore tubing exposed to atmosphere at one end and to the irrigation supply water at the other end, the fine bore tubing however being susceptible to blocking by water borne debris and/or foreign matter entering from outside during shut down periods.
One of the objects of this invention is to provide improvements whereby danger of blocking is substantially reduced. A further object of the invention is to provide for flow rate compensation such that pressure increase does not produce a corresponding flow increase.